Implementing Forth in Go and C

Summary

I first ran into Forth about 20 years ago when reading a book about designing embedded hardware. The reason I got the book back then was to actually learn more about the HW aspects, so having skimmed the Forth chapter I just registered an "oh, this is neat" mental note and moved on with my life. Over the last two decades I heard about Forth a few more times here and there, such as that time when Factor was talked about for a brief period, maybe 10-12 years ago or so. It always occupied a slot in the "weird language" category inside my brain, and I never paid it much attention. Until June this year, when a couple of factors combined fortuitously: And something clicked. I'm going to implement a Forth, because... why not? So I spent much of my free hacking time over the past two months learning about Forth and implementing two of them. Forth: the user level and the hacker level It's useful to think of Forth (at least standard Forth, not offshoots like Factor) as having two different "levels": User level: you just want to use the language to write programs. Maybe you're indeed bringing up new hardware, and find Forth a useful calculator + REPL + script language. You don't care about Forth's implementation or its soul, you just want to complete your task. Hacker level: you're interested in the deeper soul of Forth. Isn't it amazing that even control flow constructs like IF...THEN or loops like BEGIN...UNTIL are just Forth words, and if you wanted, you could implement your own control flow constructs and have them be first-class citizens, as seamless and efficient as the standard ones? Another way to look at it (useful if you belong to a certain crowd) is that user-level Forth is like Lisp without macros, and hacker-level Forth has macros enabled. Lisp can still be great and useful without macros, but macros take it to an entire new level and also unlock the deeper soul of the language. This distinction will be important when discussing my Forth implementations below. gof...